As photoconductive materials to be incorporated in electrophotographic photoreceptors there have heretofore been used inorganic substances such as selenium, cadmium sulfide, zinc oxide and amorphous silicon. These inorganic substances are advantageous in that they have excellent electrophotographic properties. In particular, these inorganic substances exhibit an extremely excellent photoconductivity, charge acceptability in a dark place and insulating properties. On the contrary, however, these inorganic substances have various disadvantages. For example, selenium photoreceptors are expensive to manufacture, have no flexibility and cannot withstand thermal or mechanical shock. Cadmium sulfide photoreceptors, which comprise a toxic material (cadmium), can cause a problem of pollution. Zinc oxide photoreceptors exhibit difficulity in image stability upon prolonged repeated use. Furthermore, amorphous silicon photoreceptors are disadvantageous in that they are extremely expensive to manufacture and need a special surface treatment to inhibit deterioration of the surface thereof.
In recent years, electrophotographic photoreceptors comprising various organic substances have been proposed to eliminate these disadvantages of such inorganic photoconductive materials. Some of these electrophotographic photoreceptors have been put into practical use. Examples of such electrophotographic photoreceptors include electrophotographic photoreceptors comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorenone-9-one as disclosed in U.S. Pat. No. 3,484,237, electrophotographic photoreceptors obtained by sensitizing poly-N-vinylcarbazole with a pyririum dye as disclosed in JP-B-48-25658 (the term "JP-B" as used herein means an "examined Japanese patent publication"), and electrophotographic photoreceptors comprising as main component an eutectic complex made of a dye and a resin as disclosed in JP-A-47-10735 (the term "JP-A" as used herein means an "unexamined published Japanese patent application disclosure").
Furthermore, active studies have been recently made on and many proposals have been made for electrophotographic photoreceptors comprising as main component an organic pigment such as perylene pigment as disclosed in U.S. Pat. No. 3,371,884, phthalocyanine pigment as disclosed in U.S. Patent 3,397,086 and 4,666,802, azlenium salt pigment as disclosed in JP-A-59-53850 and JP-A-61-212542, squarium salt pigment as disclosed in U.S. Pat. Nos. 4,396,610 and 4,644,082 and polycyclic quinone pigment as disclosed in JP-A-59-184348 and JP-A-62-28738 or the following azo pigments:
Disazo pigments as disclosed in JP-A-53-133445, JP-A-59-78356, JP-A-59-128547, JP-A-61-57945, JP-A-61-17150, JP-A-62-251752, JP-A-62-273545, JP-A-64-13555, and JP-A-64-79753, JP-B-63-18740 and JP-B-2-4893, and U.S. Pat. No. 4,504,559;
Trisazo pigments as disclosed in JP-A-58-160358 and JP-A-61-251865, and JP-B-62-39626 and JP-B-63-10419; and
Tetrakisazo pigments as disclosed in JP-A-61-182051 and JP-A-62-18565.
On the other hand, PS plates comprising a positive type sensitizing agent containing a diazo compound and a phenolic resin as main components or a negative type sensitizing agent containing an acrylic monomer or prepolymer as main component have heretofore been put into practical use as lithographic offset printing plate precursors. However, since all these printing plate precursors have a low sensitivity, these printing plate precursors are exposed to light with a film original on which an image have been previously recorded brought into close contact therewith to form printing plates. Furthermore, the progress of computer image processing technique and large capacity data storage and communication techniques have recently enabled a continuous computer operation including original input, correction, editing, layout and paging. With this computer operation, an electronic editing system capable of instantly outputting data to terminal plotters via high speed communications network or satellite communications network has been put into practical use. In particular, such an electronic editing system is in great demand in the field of newspaper printing requiring instantaneity. Furthermore, in the field of printing wherein a printing plate is reproduced as necessary based on an original stored in the form of film original, a tendency will be growing that originals are stored as digital data in large capacity recording media such as optical disc which will be developed.
However, little or no direct type printing plate precursors designed to directly receive data from the output of terminal plotters to form a printing plate have been put into practical use. Even in stations where an electronic editing system is operated, data is outputted to a silver salt system photographic film. PS plates are then exposed to light with the silver salt system photographic film brought into contact therewith to form printing plates. One of the reasons for the above described conditions is that it is difficult to provide a direct type printing plate precursor having a sensitivity high enough to form a printing plate within a practical period of time by a light source in the output plotter (e.g., He--Ne laser, semiconductor laser).
An electrophotographic light-sensitive material can be a light-sensitive material having a light sensitivity high enough to provide a direct type printing plate.
As printing plate materials (printing plate precursors) utilizing electrophotography there have been heretofore known zinc oxide-resin dispersion system offset printing plate materials as disclosed in JP-B-47-47610, JP-B-48-40002, JP-B-48-18325, JP-B-51-15766, and JP-B-51-25761. Such a printing plate material is designed to undergo an electrophographic process which comprises the formation of toner images and then a treatment which comprises impregnation with a desensitizing solution (e.g., acidic aqueous solution containing a ferrocyanide or ferricyanide) to desensitize the non-image portion. Offset printing plates thus treated have a printing resistance of 5,000 to 10,000 sheets and thus are not suitable for printing of more than 10,000 sheets. This system is also disadvantageous in that if it comprises a composition suitable for densitization, it is susceptible to deterioration in static properties and picture quality. This system is further disadvantageous in that as a desensitizing solution there must be used a harmful cyanide compound.
In an organic photoconductor-resin system printing plate material as disclosed in JP-B-37-17162, JP-B-38-7758, JP-B-46-39405, and JP-B-52-2437, an electrophotographic photoreceptor is used which comprises on a grained aluminum plate a photoconducting insulating layer comprising, e.g., an oxazole or oxadiazole compound bound with a styrene-maleic anhydride copolymer. The electrophogrphic photoreceptor is designed to undergo an electrophotographic process which comprises the formation of toner image and then dissolution and removal of the nonimage portion with an alkali-soluble organic solvent to form a printing plate.
Sato et al. of Fuji Photo Film Co., Ltd. disclose an electrophotographic printing plate precursor comprising a hydrazone compound and barbituric acid or thiobarbituric acid in JP-A-57-147656. Besides such an electrophotographic plate precursor, dye-sensitized electrophotographic printing plates as disclosed in JP-A-59-147335, JP-A-59-152456, JP-A-59-168462, and JP-A-58-145495 have been known. However, such dye-sensitized electrophotographic printing plates cannot provide a sufficient sensitivity. Thus, it has been desired to provide a photoconductor having a higher sensitivity. As an approach for solving this problem there have been known a dispersion of a charge carrier-generating compound such as phthalocyanine compound, azo compound and condensed polycyclic quinone compound in a binding resin as disclosed in JP-A-55-161250, JP-A-56-146145 and JP-A-60-17751. However, none of these approaches can provide a sufficient sensitivity or charge retention.
These electrophotographic photoreceptors can provide some improvement in mechanical properties and flexibility of the above mentioned inorganic electrophotographic photoreceptors but leave to be desired in sensitivity. These electrophotographic photoreceptors are also subject to change in electrical properties upon repeated use over many times. Thus, these electrophotographic photoreceptors cannot necessarily satisfy the requirements for electrophotographic photoreceptors.
The above mentioned electrophotographic printing plate precursors don't have sensitivity high enough to form a direct type printing plate. Even if the above mentioned electrophotographic printing plate precursors exhibit a high sensitivity, they leave to be desired in charge retention. Thus, the above mentioned electrophotographic printing plate precursors cannot necessarily satisfy the requirements.